The nature of the immunologic defect in chronic mucocutaneous candidiasis has been further defined. Measurements of plasma thymopoietin-like activity yielded essentially normal results and indicted that the lesion was not due to inadequate inductive activity from the thymus. The measurements of LIF production by antigen-stimulated cells suggested that this lymphokine was not essential for development of delayed cutaneous hypersensitivity responses. Even though lymphocytes from many patients could not produce LIF in response to antigens, in most instances mitogenic stimulation did induce LIF production. This indicates that the cells are genetically capable of producing the lymphokine and suggestes that the fundamental defect is either in generation of antigen-responsive cells or failure of antigen recognition at the cell membrane. The studies of immunologic reconstitution and resistance to infections continue. The data indicates that both "candida-positive" and "candida-negative" transfer factor has efficacy but that long lasting benefits are more likely when candida-sensitive transfer factor is used.